1. Field of the Invention
The present invention relates to an obstacle detection system for detecting an obstacle in the surroundings of the system by utilizing ultrasonic wave.
2. Description of Related Art
An obstacle detection system that detects an obstacle in the surroundings of the system by utilizing ultrasonic wave is described in, for example, JP-2003-270345A. The obstacle detection system disclosed in JP-2003-270345A can operate in a noise determination mode and an obstacle detection mode. In the noise determination mode, the obstacle detection system receives ultrasonic wave from the surroundings while not transmitting ultrasonic wave toward the surroundings from an ultrasonic sensor, recognizes the received ultrasonic wave as noise, and determines whether a voltage level of the noise is greater than or equal to a noise determination value. In the obstacle detection mode, the obstacle detection system transmits ultrasonic wave toward the surroundings from an ultrasonic sensor, receives the ultrasonic wave possibly reflected from an obstacle, and determines that the obstacle actually exists in the surrounding when a voltage level of the reflected ultrasonic wave exceeds an obstacle determination threshold. When it is determined in the noise determination mode that the voltage level of the noise is greater than or equal to the noise determination value, the obstacle detection system prohibits the operation mode from switching into the obstacle detection mode to prevent the obstacle detection operation from being performed, because there is a possibility that the noise prevents the system from detecting an obstacle with high accuracy.
According to the above described conventional technique, however, when it is determined that the voltage level of the noise is greater than or equal to the noise determination value, the operation mode is prohibited from switching into the obstacle detection mode without exception. When it is determined that the voltage level of the noise is less than the noise determination value, the operation mode is switched into the obstacle detection mode without exception.
Accordingly, when the voltage level of the noise is greater than or equal to the noise determination value, the conventional technique cannot perform the obstacle detection operation even if a situation allows obstacle detection. Such a situation is, for example, that the obstacle is located close to the system and the voltage level of the reflected ultrasonic wave is sufficiently large.